The present invention is directed toward patterning magnetic materials and, more particularly, toward patterning magnetic materials with electron beam lithography.
As the areal densities of magnetic recording media continue to increase, the physical size of the sensors and writers designed to read and write data from and to the magnetic media must decrease. As areal densities approach 1000 Gigabytes/in2, the critical dimensions of some magnetic features will be on the order of 25 nm. In order to manufacture and pattern critical dimensions on this small scale, lithography techniques capable of creating extremely fine patterns are required. One such technique is electron beam lithography, or E-beam lithography.
E-beam lithography utilizes a beam of electrons to “write”, or pattern, features in an e-beam resist. The beam of electrons is emitted from a source, then demagnified, rastered, and directed toward the e-beam resist via magnetic lenses, thus depositing energy in the desired pattern in the resist film. A problem arises, however, when e-beam lithography is utilized to pattern magnetic materials. The magnetic fields from the magnetic materials being patterned can deflect the electrons from their intended path, or may affect the lenses themselves possibly resulting in distorted structures and patterns, and errors in pattern placement on the substrate. Position errors of an e-beam generated pattern may affect the overlay (the relative position or vertical alignment) of features present in underlying process layers, making the multilayer device non-functional when features drop below a critical dimension. Some future thin-film head designs, particularly for perpendicular recording, require very tight overlay between different process layers.
Recent findings have shown that electron beam placement distortion depends strongly on magnetic material coverage on the wafer. For full-film (100%) coverage of magnetic material, the error in beam placement can be greater than 1000 nm (|mean|+3 sigma), after removing first-order terms (global magnification and rotation). On wafers having partial (25%) coverage of magnetic material, the error improves at least ten-fold to less than 100 nm. On completely non-magnetic wafers, the error in beam placement depends only on the specifications of the electron-beam lithography machine itself, which can be better than 25 nm (|mean|+3 sigma). In addition to the coverage, it is expected that the thickness and moment of magnetic material on the wafer also affect beam placement and position accuracy performance.
What is needed is an improved electron beam lithography process for patterning magnetic materials.